Display device for evaluating displayed value

ABSTRACT

A method of measuring and indicating the measured value comprises the steps of measuring a signal, exhibiting a digital indication of the measured value of the signal on a variable color light emitting diode display device, comparing the measured value with a limit to determine their relation, and controlling color of the digital indication accordingly, to simultaneously indicate the measured value of the signal, by the digital indication, and its significance, by color.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to measuring devices utilizing a variablecolor display.

[0003] 2. Description of the Prior Art

[0004] Commercially available measuring instruments with monochromaticdigital readout are capable of performing measurements and displayingresults at a relatively fast rate. However, to determine a significanceof each measured value, an operator must rapidly read displayed valuesand perform mental comparisons with predetermined limits. The task ismuch more complicated when the limits are variable.

[0005] A system for measuring radioactivity is described in U.S. Pat.No. 2,643,344, issued on Jun. 23, 1953 to Ian H. McLaren et al. Anothersystems for measuring radioactivity are described in U.S. Pat. No.2,648,015 issued on Aug. 4, 1953 to Alexander Greenfield et al., and inU.S. Pat. No. 2,682,000 issued on Jun. 22, 1954 to Joseph F. Clayton etal. Since these three patents are very similar, they are equallyauthoritative. The system for measuring radioactivity, disclosed in thethree patents, includes an analog pointer indicator having three scales,with three associated colored light bulbs, for indicating which scale isapplicable for the reading of the measured value. A mechanism forautomatic range selection is provided, which is controlled by twosolenoids, and which also controls the three associated colored lightbulbs. In response to the range selection, one of the light bulbsilluminates the indicator face with a distinctive color to indicatewhich measurement scale is applicable. After each measurement, theoperator must evaluate each measured value to determine itssignificance, mentally or otherwise.

[0006] A digital meter is disclosed in U.S. Pat. No. 2,889,518, issuedon Jun. 2, 1959 to Harold R. Hudson et al. The digital meter includes amotor, a wheel counter rotatable by the motor, a potentiometer rotatableby the motor, and a mechanical sampler (vibrator). An unknown voltage iscompared, by the sampler, with an instant reference voltage that appearson the wiper of the potentiometer. The motor keeps rotating thepotentiometer until the unknown voltage is equal to the referencevoltage. The rotation of the motor is then automatically stopped, whichalso stops the wheel counter, whose position numerically indicates thevalue of the measured voltage. The decimal point monochromatic lamps areplaced between the wheels of the counter. One of the decimal point lampsis illuminated, by manually operated range switch, to indicate by itsposition the selected measurement range.

[0007] The prior art does not contemplate a method of automaticallyevaluating the measured value. The prior art does not contemplate amethod of automatically indicating a significance of the exhibitedmeasured value, by color. The prior art does not contemplate a method ofautomatically comparing the actual measured value with stored data,representing a measurement limit, to determine their relation.

SUMMARY OF THE INVENTION

[0008] Accordingly, it is the principal object of this invention toprovide an improved method of indicating a measured value.

[0009] It is another object of the invention to provide a method ofindicating the measured value on a variable color light emitting diodedisplay.

[0010] It is still another object of the invention to provide a methodof automatically evaluating the measured value, to determine itssignificance.

[0011] It is still another object of the invention to provide a methodof comparing the measured value with a limit, to automatically determinewhether the measured value is less than the limit or more than thelimit.

[0012] It is still another object of the invention to provide a methodof comparing the measured value with two limits, to automaticallydetermine whether the measured value lies within the limits or outsidethe limits.

[0013] It is still another object of the invention to provide a methodof visually indicating the significance of the measured value.

[0014] It is still another object of the invention to provide a methodof controlling the color of the digital indication of the measuredvalue, to indicate the result of the evaluation of the measured value.

[0015] It is still another object of this invention to provide a methodof controlling the color of the digital indication of the measuredvalue, to indicate whether it lies within or without the limits.

[0016] In summary, the method of the invention comprises the steps ofmeasuring a signal, providing a digital indication of a measured valueon a variable color light emitting diode display device, comparing themeasured value with a limit, and controlling color of the digitalindication in accordance with a relation of the measured value to thelimit. Typically, the digital indication is illuminated in a first colorwhen the measured value is less than the limit, and in a second colorwhen the measured value is greater than the limit.

[0017] In the prior art measuring instruments, the measurement isperformed by the steps of automatically or manually selecting the properrange before the measurement, indicating the selected range, either bythe color of light shining on the face of an indicator, or by theposition of an illuminated decimal point lamp, performing themeasurement, and displaying the instant measured value. The operatormust then evaluate each measured value, mentally or otherwise, todetermine its significance.

[0018] In stark contradistinction, in the method of the presentinvention, each measured value is evaluated automatically, by comparingit with the stored data. The color of the indication of the measuredvalue is then controlled in accordance with the result of thecomparison. As a consequence, the operator does not need to read thosemeasured values that are exhibited in a color consistent with aninsignificant measured value (typically within the limits), and canconcentrate only on those measured values that are exhibited in a colorconsistent with a significant measured value (typically outside of thelimits).

[0019] Accordingly, the invention resides in automatically evaluatingthe measured value after the measurement, in contradistinction to theprior art, where the measurement range is appraised before themeasurement. The invention thus provides a new and unexpected result:the operator does not need to examine those measured values that areindicated, by color, as being insignificant.

[0020] Further objects of the invention will become obvious from theaccompanying drawings and their description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings in which are shown the preferred embodiments ofthe invention,

[0022]FIG. 1 is a block diagram of a digital voltmeter with a variablecolor display.

[0023]FIG. 2 is a block diagram of a variable color digital voltmeterwith an analog comparator.

[0024]FIG. 3 is a block diagram of a variable color digital voltmeterwith a digital comparator.

[0025]FIG. 4 is a simplified schematic diagram of a digital voltmeter ofthe invention.

[0026]FIG. 5 is an exemplary detail of the display on which measuredresult is displayed in yellow color on green background.

[0027]FIG. 6 is a similar detail of the display on which measured resultis displayed in yellow color on blue background.

[0028]FIG. 7 is a similar detail of the display on which measured resultis displayed in yellow color on red background.

[0029]FIG. 8 is a simplified schematic diagram of one element of avariable color display device.

[0030]FIG. 9 is a cross-sectional view, taken along the line A-A in FIG.6, revealing internal structure of a portion of a variable color displaydevice.

[0031]FIG. 10 is a schematic diagram of an analog comparator fordeveloping color control signals.

[0032]FIG. 11 is a schematic diagram of a digital comparator fordeveloping color control signals.

[0033]FIG. 12 is a detail of 13-bit digital comparator in FIG. 11.

[0034] Throughout the drawings, like character indicate like parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring now, more particularly, to the drawings, in FIG. 1 isshown a block diagram of a digital voltmeter utilizing a variable colordisplay surrounded by a variable color background area. The digitalvoltmeter includes an A/D (analog to digital) converter 51, forconverting an analog signal Vin applied to its input to digital data,and a display decoder 23 for causing the digital data to be displayed ina character format on a variable color display 11, in a manner wellknown to those skilled in the art. As will be more specifically pointedout subsequently, the display 11 includes variable color display areasarranged in a pattern and integral variable color background area. Theinvention resides in the addition of a segment color control 21 forilluminating the display areas in a suitable color and a backgroundcolor control 22 for illuminating the background area in a color relatedto the measured value. The digital voltmeter of this invention can thussimultaneously indicate the measured value, in a character format, andits significance, in a color of the display background. By way of anexample, measured value that is considered to be normal may be indicatedon green background, measured value that is slightly abnormal may beindicated on blue background, and measured value that is critical may beindicated on red background.

[0036] In FIG. 2 is shown a block diagram of a like digital voltmetercharacterized by an analog comparator 81. The input of analog comparator81 is coupled to the input of A/D converter 51 for comparing the inputsignal with predetermined limits and for developing comparison signalsaccordingly. The background color control 22 illuminates the backgroundarea of the display in accordance with the comparison signals.

[0037] In FIG. 3 is shown a block diagram of a like digital voltmetercharacterized by a digital comparator 84. The input of digitalcomparator 84 is coupled to the output of AID converter 51 for comparingthe output digital data with predetermined limits and for developingcomparison signals accordingly. The background color control 22illuminates the background area of the display in accordance with thecomparison signals.

[0038] In FIG. 4 is shown a schematic diagram of a digital voltmeter ofthis invention which includes a DVM (digital voltmeter) chip 53 formeasuring input signal Vin applied, via a resistor 90 a and decouplingcapacitor 93 a, to its HI (high) and LO (low) inputs, and for developingsegment drive signals a, b, c, d, e, f, g, and DP (decimal point) for a3 ½ digit variable color display 41 on which measured values of theinput signal may be indicated in a character format. Resistor 90 b andcapacitor 93 b, coupled to input OSCILLATORS, are provided for selectinga suitable frequency of internal oscillators. An auto zero capacitor 93c tends to decrease noise. Integrating capacitor 93 d and bufferresistor 90 c provide desired voltage swing and linearity.

[0039] The first display element of the display 41 consists of a figure‘1’ and a minus sign. The second, third, and fourth display elementsconsist of seven segments arranged in a well known 7-segment font onwhich selected characters may be exhibited in variable color. In thesecond element, the segments are designated as 31 a, 31 b, 31 c, 31 d,31 e, 31 f, and 31 g. Each display element has three color controlinputs R (red), G (green), and B (blue) designated DISPL. Each displayelement is surrounded by a variable color background area, as will bemore clearly pointed out subsequently. The background area of eachdisplay element also has three color control inputs R, G, and Bdesignated as BACK. It is obvious from the illustration that the colorcontrol inputs of the display elements and background areas arerespectively interconnected to form DISPLAY BUSES R, G, and B, forcontrolling color of all display elements uniformly, and BACKGROUNDBUSES R, G, and B, for controlling color of the entire background 32area uniformly.

[0040] FIGS. 5 to 7 are examples of displayed measured values whichconsider exemplary low limit −1.5 and high limit 1.5 (in Volts or in anyother suitable units). The invention resides in controlling the color ofbackground area 32 to indicate whether the measured value lies withinthe bounds of the low and high limits, below the low limit, or above thehigh limit. FIG. 5 shows a display on which a measured value 1.234 isdisplayed on green background, to indicate that it lies within thebounds of the low and high limits. FIG. 6 shows a display on which ameasured value −1.789 is displayed on blue background, to indicate thatit lies below the low limit. FIG. 7 shows a display on which a measuredvalue 1.956 is displayed on red background, to indicate that it liesabove the high limit. To render the illustration less complex, allmeasured values are displayed in yellow color. It will be appreciatedthat the color of the display may be also varied, to enhance thepresentation, as described in more detail in the above identifiedcopending application.

[0041] It is readily apparent that the method of displaying measuredvalues shown in FIGS. 5 to 7 is extremely advantageous. Being completelysurrounded by the background area 32, all display elements of thedisplay 41 are distinctly associated therewith. It is perfectly clearthat the color of the background area relates only to the valuesexhibited on the display elements within its boundaries, and not tovalues exhibited on display elements which may be located outside theboundaries.

[0042] Proceeding now to the detailed description, in FIG. 8 is shown asimplified schematic diagram of a one-character 7-segment variable colordisplay element with variable color background. Each display segment ofthe display element includes a triad of closely adjacent LEDs: a red LED1, green LED 2, and blue LED 3 which are adapted for producing acomposite light signal of a variable color. To facilitate theillustration, the LEDs are designated by segment letters, e. g., red LEDin the segment b is shown at 1 b, green LED in the segment d is shown at2 d, and blue LED in the segment f is shown at 3 f. The background areais comprised of background regions adjacent the display segments. Eachbackground region includes a triad of closely adjacent LEDs: a red LED4, green LED 5, and blue LED 6 which are adapted for producing acomposite light signal of a variable color. As much as possible, theLEDs in the background regions are designated by letters of adjacentdisplay segments.

[0043] The cathodes of all red, green, and blue display LED triads areinterconnected in each display segment and electrically connected torespective inputs a, b, c, d, e, f, g, and DP (decimal point) which maybe coupled to the outputs of DVM chip 53 viewed in FIG. 4. The anodes ofall display red LEDs 1 a, 1 b, 1 c, 1 d, 1 e, 1 f, 1 g, and 1 i arecommonly coupled to an electric path referred to as a display red bus12. The anodes of all display green LEDs 2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2g, and 2 i are commonly coupled to a like electric path referred to as adisplay green bus 13. The anodes of all display blue LEDs 3 a, 3 b, 3 c,3 d, 3 e, 3 f, 3 g, and 3 i are commonly coupled to a like electric pathreferred to as a display blue bus 14.

[0044] In a similar fashion, the anodes of all background red LEDs 4 a,4 b, 4 c, 4 d, 4 e, 4 f, 4 g, and 4 h are commonly coupled to anelectric path referred to as a background red bus 16. The anodes of allbackground green LEDs 5 a, 5 b, 5 c, 5 d, 5 e, 5 f, 5 g, and 5 h arecommonly coupled to a like electric path referred to as a backgroundgreen bus 17. The anodes of all background blue LEDs 6 a, 6 b, 6 c, 6 d,6 e, 6 f, 6 g, and 6 h are commonly coupled to a like electric pathreferred to as a background blue bus 18. The cathodes of all red, green,and blue LED triads in each background region are grounded.

[0045] The display red bus 12 is connected to the output of anon-inverting buffer 25 a capable of sourcing sufficient current toilluminate all display red LEDs. The display green bus 13 is connectedto the output of a like buffer 25 b. The display blue bus 14 isconnected to the output of a like buffer 25 c. The background red bus 16is connected to the output of a like buffer 25 d. The background greenbus 17 is connected to the output of a like buffer 25 e. The backgroundblue bus 18 is connected to the output of a like buffer 25 f. It wouldbe obvious to those skilled in the art that current limiting resistorsmay be connected in series with all LEDs in the circuit to constraincurrent flow.

[0046] The operation of the display element shown in FIG. 4 will be nowexplained on example of illuminating digit ‘1’ in yellow color. Toexhibit decimal number ‘1’, low voltage levels are applied to the inputsb and c, to illuminate equally designated segments, and high voltagelevels are applied to all remaining inputs, to extinguish all remainingsegments.

[0047] To illuminate the display element in yellow color, the colorcontrol inputs R and G of the display buses are raised to a high logiclevel, while color control input B is maintained at a low logic level.As a result, the outputs of buffers 25 a and 25 b rise to a high logiclevel. The current flows from the output of buffer 25 a, via display redbus 12 and red LED 1 b, to the input b, and, via red LED 1 c, to theinput c. The current also flows from the output of buffer 25 b, viadisplay green bus 13 and green LED 2 b, to the input b, and, via greenLED 2 c, to the input c. As a result of blending light signals of redand green colors in the segments b and c, the segments illuminate insubstantially yellow color, creating a visual impression of a character‘1’.

[0048] To illuminate the background area in green color, the colorcontrol input G of the background buses is raised to a high logic level,while the remaining color control inputs R and B are low. As a result,the output of buffer 25 e rises to a high logic level. The current flowstherefrom, via background green bus 17 and green LEDs 5 a, 5 b, 5 c, 5d, 5 e, 5 f, 5 g, and 5 h in all background regions, to ground. Theentire background area illuminates in green color.

[0049] To illuminate the background area in blue color, the colorcontrol input B of the background buses is raised to a high logic level,while the remaining color control inputs R and G are low. As a result,the output of buffer 25 f rises to a high logic level. The current flowstherefrom, via background blue bus 18 and blue LEDs 6 a, 6 b, 6 c, 6 d,6 e, 6 f, 6 g, and 6 h in all background regions, to ground. The entirebackground area illuminates in blue color.

[0050] To illuminate the background area in red color, the color controlinput R of the background buses is raised to a high logic level, whilethe remaining color control inputs G and B are low. As a result, theoutput of buffer 25 d rises to a high logic level. The current flowstherefrom, via background red bus 16 and red LEDs 4 a, 4 b, 4 c, 4 d, 4e, 4 f, 4 g, and 4 h in all background regions, to ground. The entirebackground area illuminates in red color.

[0051] An important consideration has been given to physical arrangementof the LEDs in the display areas and background regions, as illustratedin FIG. 9. Display red LED 1 f, green LED 2 f, and blue LED 3 f aredisposed on a support 10 in a display light blending cavity 8 f andcompletely surrounded by transparent light scattering material 34. Whenforwardly biased, the LEDs If, 2 f, and 3 f emit light signals of red,green, and blue colors, respectively, which are blended by passingthrough light scattering material 34, acting to disperse the lightsignals, to form a composite light signal that emerges at the uppersurface 35 f. The color of the composite light signal may be controlledby varying the portions of red, green, and blue light signals. Displayred LED 1 b, green LED 2 b, and blue LED 3 b are similarly disposed in adisplay light blending cavity 8 b and may be similarly activated.

[0052] In a similar fashion, background red LED 4 g, green LED 5 g, andblue LED 6 g are disposed on the support 10 in a background lightblending cavity 9 g and surrounded by transparent light scatteringmaterial 34. When forwardly biased, the LEDs 4 g, 5 g, and 6 g emitlight signals of red, green, and blue colors, respectively, which areblended by passing through the light scattering material 34 to form acomposite light signal of a composite color that emerges at the uppersurface 36 g.

[0053] The display light blending cavities are optically separated fromadjacent background light blending cavities by opaque walls. The displaylight blending cavity 8 f is defined by walls 7 a and 7 b. The wallshave generally smooth inclined surfaces defining an obtuse angle withthe support 10. The walls 7 b and 7 c similarly define a backgroundlight blending cavity 9 g therebetween. In a similar fashion, thedisplay light blending cavity 8 b is defined by the walls 7 c and 7 d.The width of the top surfaces of the opaque walls is uniform anddistinctly less than the width of the display areas or backgroundregions so as to minimize the boundaries therebetween. The top surfacesof the opaque walls and top surfaces of the display areas and backgroundregions are in the same plane to allow wide angle observation of thedisplay device. Although the walls and light blending cavities are shownto be of certain shapes and dimensions, it is envisioned that they maybe modified and rearranged.

[0054] In FIG. 10, the input signal Vin is applied to the interconnectedinputs of two analog comparators 82 a, 82 b in a classic ‘window’comparator configuration. When the input voltage is lower than the lowvoltage limit Vlo, set by a potentiometer 92 a, the output of comparator82 a drops to a low logic level, thereby forcing the output of aninverter 65 a to rise to a high logic level to develop active colorcontrol signal B.

[0055] When the input voltage is higher than the high voltage limit Vhi,set by a potentiometer 92 b, the output of comparator 82 b drops to alow logic level, thereby forcing the output of an inverter 65 b to riseto a high logic level to develop active color control signal R.

[0056] When the input voltage is between the low voltage limit Vlo andhigh voltage limit Vhi, the outputs of comparators 82 a, 82 b rise to ahigh logic level (pull-up resistors 91 a, 91 b ensure correct high andlow levels), thereby causing the output of AND gate 66 to rise to a highlogic level to develop active color control signal G. The outputs B, G,and R may be respectively coupled to like inputs of the background busesin FIG. 4 to cause the background area 32 to illuminate in one of threecolors in accordance with the range in which the measured voltage lies.

[0057] In FIG. 11 is shown a schematic diagram of a digital voltmeterwith a comparator for developing color control signals. A DVM chip 54measures input signal Vin applied via a resistor 90 f to its input INand develops at its outputs A, B, C, D of Units, Tens, Hundreds, andThousand digital data corresponding to the value of measured inputsignal. The input INIT CONV (initiate conversion) is tied to a highlogic level for causing the DVM chip to measure continuously. The outputdigital data are simultaneously applied to the inputs A0 to A12 of a13-bit digital comparator 85 a and to the inputs A0 to A12 of a likecomparator 85 b. Two 8-bit latches 63 a, having its outputs Q0 to Q7respectively coupled to the inputs B0 to B7 of comparator 85 a, and 63b, having its outputs Q0 to Q4 respectively coupled to the inputs B8 toB12 of comparator 85 a, are provided for storing a digitalrepresentation of a low limit. Two like latches 63 c, having its outputsQ0 to Q7 respectively coupled to the inputs B0 to B7 of comparator 85 b,and 63 d, having its outputs Q0 to Q4 respectively coupled to the inputsB8 to B12 of comparator 85 b, are provided for storing a digitalrepresentation of a high limit. The comparator 85 a effects a comparisonof the output digital data with the low limit and develops comparisonsignals accordingly. The comparator 85 b effects a comparison of theoutput digital data with the high limit and develops comparison signalsaccordingly. It would be obvious that data in the latches may be readilychanged by applying new data to the inputs D0 to D7 and clocking sameinto the latches (not shown).

[0058] When the output digital data of DVM chip 54 are less than the lowlimit, the output ‘<’ of comparator 85 a rises to a high logic level togenerate an active color control signal B. When the digital data aregreater than the high limit, the output ‘>’ of comparator 85 b rises toa high logic level to generate an active color control signal R. Whenthe digital data are within the bounds of the low and high limits, oneof the outputs ‘=’ and ‘>’ of comparator 85 a, which are gated by an ORgate 60 a, and one of the outputs ‘<’ and ‘=’ of comparator 85 b, whichare gated by an OR gate 60 b, rise to a high logic level to force bothinputs of an AND gate 66 b to rise to a high logic level. As aconsequence, the output of OR gate 66 b rises to a high logic level togenerate active color control signal G. The comparison outputs B, G, andR may be respectively coupled to like inputs of the background buses inFIG. 4 for causing the background area 32 of the display 41 toilluminate either in blue color when the measured value is less than thelow limit, in red color when the measured value is greater than the highlimit, or in green color when the measured value is within the bounds ofthe low and high limits. It would be obvious that the color sequencescould be readily changed by differently interconnecting the comparisonoutputs with the background color control inputs.

[0059]FIG. 12 is a detail of one of 13-bit digital comparators 85 a, 85b in FIG. 11. It will be appreciated that both digital comparators 85 a,85 b may be substantially same. The comparison inputs ‘<’, ‘=’, and ‘>’of four 4-bit digital comparators 86 a, 86 b, 86 c, and 86 d arerespectively coupled to like preceding outputs, in a manner wellunderstood by those skilled in the art, to extend the comparison rangeto 13 bits.

[0060] The invention may be now briefly summarized. A method ofindicating a measured value was disclosed that comprises the steps ofmeasuring a signal, exhibiting a character indication of the measuredvalue on a variable color light emitting diode display device, comparingthe measured value with a limit to determine their relation, andcontrolling color of the character indication accordingly.

[0061] It would be obvious that persons skilled in the art may resort tomodifications in the construction of the preferred embodiments shownherein, without departing from the scope, as defined in the appendedclaims, and the spirit of the invention. It is contemplated that theprinciples of the invention may be also applied to numerous diversetypes of display devices, such as liquid crystal devices, plasmadevices, luminescent devices, cathode ray tube devices, and the like.CORRELATION TABLE This is a correlation table of reference charactersused in the drawings herein, their descriptions, and examples ofcommercially available parts.  # DESCRIPTION EXAMPLE  1 display red LED 2 display green LED  3 display blue LED  4 background red LED  5background green LED  6 background blue LED  7 opaque wall  8 displaylight blending cavity  9 background light blending cavity 10 support 11variable color display 12 display red bus 13 display green bus 14display blue bus 16 background red bus 17 background green bus 18background blue bus 21 segment color control 22 background color control23 display decoder 25 non-inverting buffer 74LS244 31 display segment 32background area 34 light scattering material 35 top surface of displayarea 36 top surface of background area 41 3½ digit variable colordisplay 51 A/D converter 53 Teledyne DVM chip TSC7107 54 Teledyne DVMchip TSC8750 60 2-input OR gate 74HC32 63 8-bit latch 74HC373 65inverter 74HC04 66 2-input AND gate 74HC08 81 analog comparator 82analog comparator chip LM339 84 digital comparator 85 13-bit digitalcomparator 86 4-bit digital comparator 74HC85 90 resistor 91 resistor 92potentiometer 93 capacitor

What I claim is:
 1. A method of indicating a measured value, the methodcomprising: measuring a signal for obtaining a measured value of thesignal; exhibiting a character indication of said measured value, on avariable color light emitting diode display device, said display devicebeing capable of controlling color of said character indication inresponse to a color control signal; comparing said measured value withstored data; developing a color control signal in accordance with therelation of said measured value to said data; applying said colorcontrol signal for controlling the color of said character indicationaccordingly.
 2. The method as recited in claim 1 wherein said comparingstep is performed in a digital fashion.
 3. The method as recited inclaim 1 wherein: a. said developing step comprises: developing a firstcolor control signal when said measured value is less than the value ofsaid data; developing a second color control signal when said measuredvalue is greater than the value of said data; b. said applying stepcomprises: applying said first color control signal, when said firstcolor control signal is developed, to said display device forilluminating said character indication in a first color; and applyingsaid second color control signal, when said second color control signalis developed, to said display device for illuminating said characterindication in a second color.
 4. The method as recited in claim 1wherein: a. said comparing steps comprises: comparing said measuredvalue with a first limit to determine their relation; comparing saidmeasured value with a second limit to determine their relation; thevalue of said first limit being less than the value of said secondlimit; b. said developing step comprises: developing a first colorcontrol signal when said measured value is either less than said firstlimit or greater than said second limit; developing a second colorcontrol signal when said measured value is simultaneously greater thansaid first limit and less than said second limit; c. said applying stepcomprises: applying said first color control signal, when said firstcolor control signal is developed, to said display device forilluminating said character indication in a first color; and applyingsaid second color control signal, when said second color control signalis developed, to said display device for illuminating said characterindication in a second color.
 5. The method as recited in claim 1wherein: a. said comparing steps comprises: comparing said measuredvalue with a first limit to determine their relation; comparing saidmeasured value with a second limit to determine their relation; thevalue of said first limit being less than the value of said secondlimit; b. said developing step comprises: developing a first colorcontrol signal when said measured value is less than said first limit;developing a second color control signal when said measured value issimultaneously greater than said first limit and less than said secondlimit; developing a third color control signal when said measured valueis greater than said second limit; c. said applying step comprises:applying said first color control signal, when said first color controlsignal is developed, to said display device for illuminating saidcharacter indication in a first color; applying said second colorcontrol signal, when said second color control signal is developed, tosaid display device for illuminating said character indication in asecond color; and applying said third color control signal, when saidthird color control signal is developed, to said display device forilluminating said character indication in a third color.
 6. A method ofautomatically evaluating a measured value and of simultaneouslyindicating the measured value and its evaluation, the method comprising:measuring a signal for obtaining a measured value of the signal;exhibiting a digital indication of said measured value, on a variablecolor light emitting diode display device, said display device beingcapable of controlling color of said digital indication in response to acolor control signal; comparing the value of said digital indicationwith stored data; developing a color control signal in accordance withthe relation of said digital indication to said data; applying saidcolor control signal to said display device for controlling the color ofsaid digital indication accordingly.
 7. The method as recited in claim 6wherein said comparing step is performed in a digital fashion.
 8. Amethod of automatically evaluating a measured value and ofsimultaneously indicating the measured value and its evaluation, themethod comprising: measuring a signal for obtaining a measured value ofthe signal; exhibiting a digital indication of said measured value, on avariable color light emitting diode display device, said display devicebeing capable of controlling color of said digital indication inresponse to a color control signal; comparing the value of said digitalindication with a first limit and with a second limit, the value of saidfirst limit being less than the value of said second limit; developing afirst color control signal when said value of said digital indication iseither less than said first limit or greater than said second limit;developing a second color control signal when said value of said digitalindication is simultaneously greater than said first limit and less thansaid second limit; applying said first color control signal, when saidfirst color control signal is developed, to said display device forilluminating said digital indication in a first color; and applying saidsecond color control signal, when said second color control signal isdeveloped, to said display device for illuminating said digitalindication in a second color.
 9. The method as recited in claim 8wherein said first limit is a low measurement limit other than a rangelimit, and said second limit is a high measurement limit other than arange limit.
 10. The method as recited in claim 8 wherein said firstlimit and said second limit are stored in a memory, and said value ofsaid digital indication is compared with the values stored in saidmemory.
 11. A method of automatically evaluating a measured value and ofsimultaneously indicating the measured value and its evaluation, themethod comprising: measuring a signal for obtaining a measured value ofthe signal; exhibiting a digital indication of said measured value, on avariable color light emitting diode display device, said display devicebeing capable of controlling color of said digital indication inresponse to a color control signal; comparing the value of said digitalindication with a first limit and with a second limit, the value of saidfirst limit being less than the value of said second limit; developing afirst color control signal when said value of said digital indication isless than said first limit; developing a second color control signalwhen said value of said digital indication is simultaneously greaterthan said first limit and less than said second limit; developing athird color control signal when said value of said digital indication isgreater than said second limit; applying said first color controlsignal, when said first color control signal is developed, to saiddisplay device for illuminating said digital indication in a firstcolor; applying said second color control signal, when said second colorcontrol signal is developed, to said display device for illuminatingsaid digital indication in a second color; and applying said third colorcontrol signal, when said third color control signal is developed, tosaid display device for illuminating said digital indication in a thirdcolor.
 12. A method of automatically evaluating a measured value and ofsimultaneously indicating the measured value and its evaluation, themethod comprising: measuring a signal for obtaining a measured value ofthe signal; exhibiting a digital indication of said measured value, on avariable color light emitting diode display device, said display devicebeing capable of controlling color of said digital indication inresponse to a color control signal; comparing the value of said digitalindication with a low limit and a with high limit, and developing acolor control signal accordingly; applying said color control signal tosaid display device for illuminating said digital indication in a firstcolor when said value of said digital indication lies within the boundsof said low limit and said high limit; and applying said color controlsignal to said display device for illuminating said digital indicationin a second color when said value of said digital indication liesoutside the bounds of said low limit and said high limit.
 13. The methodas recited in claim 12 wherein said low limit and said high limit arestored in a memory, and said value of said digital indication iscompared with the values stored in said memory.
 14. A method ofautomatically evaluating a measured value and of simultaneouslyindicating the measured value and its evaluation, the method comprising:measuring a signal for obtaining a measured value of the signal;exhibiting a digital indication of said measured value, on a variablecolor light emitting diode display device, said display device beingcapable of controlling color of said digital indication in response to acolor control signal; comparing the value of said digital indicationwith a low limit and a with high limit, and developing a color controlsignal accordingly; applying said color control signal to said displaydevice for illuminating said digital indication in a first color whensaid value of said digital indication is less than said low limit;applying said color control signal to said display device forilluminating said digital indication in a second color when said valueof said digital indication lies within the bounds of said low limit andsaid high limit; and applying said color control signal to said displaydevice for illuminating said digital indication in a third color whensaid value of said digital indication is greater than said high limit.15. A method of automatically evaluating a measured value and ofsimultaneously indicating the measured value and its evaluation, themethod comprising: measuring a signal for obtaining a measured value ofthe signal; exhibiting a digital indication of said measured value, on avariable color light emitting diode display device, said display devicehaving a color control input for controlling color of said digitalindication; comparing the value of said digital indication with storeddata and developing a comparison output indicative of their relation;and coupling said comparison output to said color control input.
 16. Themethod as recited in claim 15 wherein said color control input iscompatible with logic level signals, and said comparison output iscompatible with logic level signals.
 17. The method as recited in claim15 wherein said comparing step comprises: comparing the value of saiddigital indication with a first limit and a second limit; developing afirst comparison output when the value of said digital indication iswithin said first limit and said second limit; and developing a secondcomparison output when the value of said digital indication is outsideof said first limit and said second limit.
 18. The method as recited inclaim 15 wherein said comparing step comprises: comparing the value ofsaid digital indication with a first limit and a second limit;developing a first comparison output when the value of said digitalindication is less than said first limit; developing a second comparisonoutput when the value of said digital indication is simultaneouslygreater than said first limit and less than said second limit; anddeveloping a third comparison output when the value of said digitalindication is greater than said second limit.
 19. A method ofautomatically evaluating a measured value and of simultaneouslyindicating the measured value and its evaluation, the method comprising:measuring a signal for obtaining a measured value of the signal;exhibiting a digital indication of said measured value, on a variablecolor light emitting diode display device, said display device havingtwo color control inputs for illuminating said digital indication in oneof two colors; comparing the value of said digital indication with a lowlimit and a high limit and developing two comparison outputs indicativeof their relation; and coupling said two comparison outputs to said twocolor control inputs, respectively.
 20. A method of automaticallyevaluating a measured value and of simultaneously indicating themeasured value and its evaluation, the method comprising: measuring asignal for obtaining a measured value of the signal; exhibiting adigital indication of said measured value, on a variable color lightemitting diode display device, said display device having three colorcontrol inputs for illuminating said digital indication in one of threecolors; comparing the value of said digital indication with a low limitand a high limit and developing three comparison outputs indicative oftheir relation; and coupling said three comparison outputs to said threecolor control inputs, respectively.